The present invention relates to a microphone system which may be used with an in-the-ear hearing aid system. In particular, the present invention relates to an adjustable microphone system, which may be used with an in-the-ear hearing aid, which allows the wearer to switch between a non-directional (or omni-direction) mode or a directional mode.
Typical hearing aids either include a non-directional or directional hearing aid system. A non-directional hearing aid system allows the wearer to pickup sounds from any direction. When a hearing aid wearer is trying to carry on a conversation within a crowded room, a non-directional hearing aid system does not allow the wearer to easily differentiate between the voice of the person the wearer is talking to and background or crowd noise. A directional hearing aid helps the wearer to hear the voice of the person he or she is having a conversation with, while reducing the miscellaneous crowd noise present within the room.
Traditionally, directional hearing aids are implemented with a single microphone having inlets to cavities located in front and back of a diaphragm. Directionality with a single microphone is accomplished with an acoustic resistor placed across a hole in the back inlet of the microphone acting in combination with the compliance formed by the volume of air behind the diaphragm. This system is termed a first order pressure gradient directional microphone because the microphone output is a function of the pressure differential across the diaphragm.
One measure of the amount of directivity of a directional hearing aid system is a polar directivity pattern 10 as shown in FIG. 1. The polar directivity pattern 10 shows the amount of pickup at a specific frequency (in terms of attenuation in dB) of a directional hearing aid system as a function of azimuth angle of sound incidence. Accurate measurement of a polar directivity pattern requires an anechoic chamber. An anechoic chamber is an enclosed room that has minimum reflection of sound from its inner wall surfaces and that attenuates ambient sounds entering from the outside. Thus, inside an anechoic chamber, the direction of arrival of sound can be controlled so that it comes from only one specific angle of incidence.
A cardioid or heart-shaped polar pattern produces a directivity index of about 3-4 dB. The directivity index is the ratio of energy arriving from in front of the hearing aid wearer to the random energy incident from all directions around and imaginary sphere with the hearing aid at its center. However, a super cardioid polar pattern 14, as shown in FIG. 2, which can also be obtained with a first order pressure gradient directional hearing aid microphone, produces a 5-6 dB directivity index. It has been found that producing a super-cardioid polar pattern 14 requires 1.72 times greater front-to-rear microphone port spacing than a cardioid polar pattern 12. Because of limited space, a super cardioid directivity pattern is more difficult to achieve using a single directional microphone in a full-concha custom in-the-ear hearing device.
Conventional behind-the-ear type hearing aids have included a main body and a hook extending from the main body and arrange to engage the upper end of the ear lobe of the wearer to hang the main body on the ear. Known versions of behind-the-hearing aids that had variable amounts of directionality use mechanical shutters or valves to adjust the amount of directionality. For example, see U.S. Pat. No. 3,798,390 to Gage et al.; U.S. Pat. No. 3,836,732 to Johanson et al.; and U.S. Pat. No. 4,051,330 to Cole. Other known behind-the-ear hearing aid systems, such as U.S. Pat. No. 5,214,709 to Ribic suggests a behind-the-ear hearing aid system which includes the use of more than one non-directional microphone to make a directional microphone behind-the-ear hearing aid system.
Persons with an unaidable unilateral hearing loss or persons having one ear that cannot be aided with a hearing aid (known as a dead ear) and one ear with some aidable hearing loss often have great difficulty communicating in high noise levels. In such hearing loss configurations, this difficulty occurs because of the loss of the auditory system""s normal ability to suppress noise, which is the expected result of the cross-correlation capability of the brain using the balanced, fused, binaurally-processed inputs from the two normal cochleas of a normal hearing person.
Contralateral Routing Of Signals (CROS) and Bilateral Routing of Signals (BiCROS) hearing aids, respectively, are often employed for such persons since they often have great difficulty wearing only one hearing aid. In essence, two instrument CROS and BiCROS systems take sound from the bad ear, process it, then send the processed sound via hard wire, RF, or induction transmission to a receiver in the other ear.
CROS systems are utilized for individuals with one unaidable ear and one ear with normal hearing or a mild hearing loss. A microphone is worn on the unaidable ear, and the receiver is worn on the better ear. BiCROS systems are utilized for individuals having one unaidable ear and one ear needing amplification. In the BiCROS system, a microphone is worn on each ear, and the receiver is worn on the better ear. CROS and BiCROS hearing aids overcome the loss of about 6 dB caused by the head blocking and diffracting sounds incident to one ear (the dead side) as they cross over to the better ear.
It is desirable to have an in-the-ear hearing aid system which allows the wearer to switch between a non-directional (omni-directional) and a directional hearing aid mode. Further, it is desirable to have an in-the-ear hearing aid system having an adjustable directional microphone system, wherein the adjustable directional microphone system. Further, it is desirable to have an in-the-ear hearing aid microphone system having an adjustable directional microphone system to allow compensation for small ears where the microphone inlets cannot be spaced far apart. It is also desirable to have an in-the-ear hearing aid microphone system which allows the in-the-ear hearing aid microphone system to be adjusted for manufacturing tolerances between the individual microphones. Finally, it is desirable to have a CROS or BiCROS hearing aid which offers a switched directional/non-directional capability.
The present invention includes an apparatus for use as an in-the-ear hearing aid. The apparatus includes a housing having a shell and a face plate, wherein the shell is molded to custom fit a hearing aid wearer""s ear. A first non-directional microphone system is included having a first inlet opening in the face plate for receiving sound, and having a first output signal representative of the sound received. A second non-directional microphone system is included having a second inlet opening in the face plate for receiving sound and having a second output signal representative of the sound received. A switch mechanism is provided having an operator extending through the housing for switching the in-the-ear hearing aid between a non-directional mode and a directional mode.
The switch has an open position and a closed position. When the switch is in the closed position, the in-the-ear hearing aid operates in a directional mode. When the switch is in an open position, the in-the-ear hearing aid operates in a non-directional mode.
The apparatus may further include means for summing, selectively coupled to the first non-directional microphone system and the second non-directional microphone system, having a summed output signal representative of the sum of the first output signal and the second output signal. When the hearing aid is in the directional mode, the output signal has a polar directivity pattern representative of the summed output signal, the means for summing may further comprise means for adjusting the polar directivity pattern of the summed output signal. The means for adjusting the polar directivity pattern may include an inverting amplifier coupled to the second microphone system, and an adjustable low pass filter coupled to the inverting amplifier. In one embodiment, the adjustable phase delay includes an adjustable phase delay having an adjustable capacitor. The means for adjusting the polar directivity may further include an adjustable amplifier coupled to the second microphone system.
In one embodiment, the first inlet opening and the second inlet opening are relatively close together. In one particular embodiment, the first inlet opening and second inlet opening are less than one/half inch apart, and the first inlet opening and the second inlet opening are located in approximately the same plane, which is generally horizontal to the ground when the in-the-ear hearing aid is located in a wearer""s ear.
In another embodiment, the present invention includes a microphone system for use with an in-the-ear hearing aid. The system includes a first non-directional microphone system having a first inlet opening for receiving sound and having a first output signal representative of the sound received. A second non-directional microphone system is included having a second inlet opening for receiving sound having a second output signal representative of the sound received. Means are provided for coupling the first non-directional microphone system to the second non-directional microphone system for switching the in-the-ear hearing aid between a non-directional mode and a directional mode.
The means for coupling may be a switch having a closed position and an open position, and wherein when the switch is in the open position, the in-the-ear hearing aid is in the non-directional mode, and when the switch is in a closed position, the in-the-ear hearing aid is in a directional mode.
The second non-directional microphone system may further include means for inverting the second output signal. The second non-directional microphone system may further include means for adjusting the phase delay of the second output signal relative to the first output signal. The means for adjusting the phase delay may include a low pass filter having an adjustable capacitor. Further, the second non-directional microphone system may further include means for adjusting the amplitude of the second output signal relative to the first output signal.
The present invention may include means for summing the first output signal and the second output signal. The means for summing may have an output coupled to an amplifier. The amplifier may include a phase delay.
In yet another embodiment, the present invention may integrate two switched directional/non-directional microphone systems as described above into a two instrument, in-the-ear CROS or BiCROS hearing aid. The connection between the two instruments of the CROS or BiCROS hearing aid may be made via a hard wire connection, RF, or induction transmission.